cockatiels inactive

i have two cockatiels, since yesturday, both have been very larthargic, just sleeping all day with ruffled feathers as if they are cold, when it has been 25 degrees.some loss of appetite, eating occasionaly,seem happy enough, but something bothering them enough not to eat thier fav treat of grainy bread, or whistle their theme tunes. do they have a cold? No mucus, or laboured breathing. no redness of nose and eyes, dropping seem normal. but less regular due to less eating.